1. Field of the Invention
The present invention relates to an ink jet apparatus having a piezoelectric ceramic arrangement comprising ink channels separated by walls and filled with ink. The walls of the ink channels are selectively deformed by the piezoelectric effect to vary the volumes of the channels so that the ink therein will be jetted out through the nozzles corresponding to those channels.
2. Description of the Related Art
The above type of ink jet apparatus has been conventionally used in ink jet printers. A first example of a typical prior art ink jet apparatus is outlined below with reference to FIG. 6. In FIG. 6, each ink chamber 70 is formed by a housing 72 including side walls 74 equipped with piezoelectric ceramic devices 76. Electrodes 77 are furnished on both sides of each piezoelectric ceramic device 76 and are connected to a driving circuit 79.
When the driving circuit 79 applies a driving voltage to the electrodes 77, the piezoelectric ceramic device 76 attached thereto is deformed accordingly. With the piezoelectric ceramic device 76 deformed, the side wall 74 is deformed into a shape indicated by the dashed line in FIG. 6, thereby reducing the volume of the ink chamber 70. The reduction in the volume of the ink chamber 70 causes the ink therein to jet out as an ink droplet 80 through a nozzle 82.
Thereafter, with the driving voltage removed, the piezoelectric ceramic device 76 returns to its original shape and thus increases the volume of the ink chamber 70. The increase in the volume of the ink chamber 70 introduces additional ink thereinto through an ink conduit 84. Typically, ink jet printers comprise numerous ink chambers 70 when manufactured.
A second example of a typical prior art ink jet apparatus is outlined below with reference to FIG. 7. In FIG. 7, an ink jet printer head 1 comprises a piezoelectric ceramic plate 2, a cover plate 3, a nozzle plate 31 and a substrate 41.
The piezoelectric ceramic plate 2 has a plurality of grooves 8. Side walls 11 defining the grooves 8 are polarized in the direction shown by arrow 5. The grooves 8 are of a uniform depth and are parallel. The grooves 8 become gradually shallower as they approach an edge 15 of the piezoelectric ceramic plate 2. Near the edge 15, the grooves 8 merge into shallow grooves 16. Inside the grooves 8, the upper half of each of the side walls 11 is covered with a metal electrode 13 formed thereon by sputtering or by other suitable processes. Inside the shallow grooves 16, the entire side walls and the bottoms are covered with metal electrodes 9 deposited by sputtering or by other suitable processes. In this arrangement, the metal electrodes 13 formed on both sides of each groove 8 are connected electrically to the metal electrodes 9 furnished over the shallow grooves 16.
The cover plate 3 is made of ceramic or plastic resin. On the cover plate 3, ink inlet ports 21 and manifolds 22 are formed by grinding or by cutting. The side of the piezoelectric ceramic plate 2 having the grooves 8 formed thereon is bonded using epoxy resin adhesive or the like to the side of the cover plate 3 having the manifolds 22 machined thereon. Covering the top of the grooves 8 in this manner with the plate 3 forms a plurality of ink channels 12 (FIG. 9) spaced apart crosswise in the ink jet printer head 1. Each ink channel 12 has a rectangular cross section and is long and narrow in shape. All ink channels 12 are filled with ink during operation.
The nozzle plate 31 is attached to one end of the piezoelectric ceramic plate 2 and the cover plate 3. The nozzle plate 31 has nozzles 32 formed in the positions corresponding to the ink channels 12. The nozzle plate 31 is made of plastic such as polyalkylene (e.g., ethylene), terephthalate, polyimide, polyether imide, polyether ketone, polyether sulfone, polycarbonate or cellulose acetate.
A substrate 41 is bonded using epoxy resin adhesive or the like to the surface opposite to the side of the piezoelectric ceramic plate 2 having the grooves 8. The substrate 41 has conductive layer patterns 42 corresponding to the positions of the ink channels 12. The metal electrodes 9 at the bottoms of the shallow parallel grooves 16 are connected to the conductive layer patterns 42 by conductors 43 deposited by wire bonding.
The control section of the prior art apparatus is described with reference to FIG. 8, which is a schematic diagram of the control section. Each of the conductive layer patterns 42 on the substrate 41 is connected individually to an LSI chip 51. Also connected to the LSI chip 51 are a clock line 52, a data line 53, a voltage line 54 and a grounding line 55. Given continuous clock pulses through the clock line 52 as well as data from the data line 53, the LSI chip 51 decides through which of the nozzles 32 ink droplets are to be jetted out. Based on its decision, the LSI chip 51 selectively applies the voltage V of the voltage line 54 to the conductive layer patterns 42 connected to the metal electrodes 13 that belong to the target ink channels 12. The LSI chip 51 also applies a zero voltage of the grounding line 55 to those conductive layer patterns 42 connected to the metal electrodes 13 associated with ink channels 12 that are not targetted for jetting.
The operation of the ink jet printer head 1 is described with reference to FIGS. 9 and 10. Suppose that, given appropriate data, the LSI chip 51 decides that an ink droplet is to be jetted out from an ink channel 12b. Then, a positive driving voltage V is applied to metal electrodes 13e and 13f while metal electrodes 13d and 13g are connected to ground. This develops a driving electric field in a side wall 11b in the direction of arrow 14b and another driving electric field in a side wall 11c in the direction of arrow 14c, as illustrated in FIG. 10. Because the directions 14b and 14c of the driving electric fields are each perpendicular to the direction of polarization 4, the side walls 11b and 11c are deformed rapidly toward the inside of the ink channel 12b due to the piezoelectric thickness slip effect. The side wall deformation reduces the volume of the ink channel 12b and rapidly raises the ink pressure therein. The resulting pressure wave causes an ink droplet to be jetted out through the nozzle 32 (FIG. 7) connected to the ink channel 12b.
One disadvantage of the prior art ink jet apparatus is that the nozzle 32 is located inside each ink channel 12, i.e., the position of the nozzle 32 is not fixed definitively relative to the ink channel 12. The center positions of the nozzles 32 may or may not be aligned with the centers of the ink channels 12. The flow rate of ink at the center of each ink channel 12 can differ from the flow rate off the center thereof. The differences in ink flow rate can translate into different jet speeds of ink droplets from the nozzles, causing the print speed to vary from one ink jet printer head 1 to another. Such speed discrepancies can render the ink jet printer head 1 nonconducive to mass-production.
On the same ink jet printer head 1, the center positions of individual nozzles 32 may or may not be aligned with the centers of the corresponding ink channels 12. This means that the jet speed of ink droplets can vary from nozzle to nozzle 32 on the same printer head. The jet speed discrepancies can lead to a serious deterioration of print quality with the ink jet printer head 1. In some cases, the printer head does not function outright. As a result, there can be many defective ink printer heads if the printer heads are mass-produced.
On the prior art ink jet apparatus, the nozzles 32 are thought to jet out ink droplets in more stable quantities and at more stable speeds when narrowed progressively (i.e, tapered) toward the ink jetting side from the ink channel side than when shaped otherwise (i.e., widened progressively toward the ink jetting side from the ink channel side, or bored straight to have the same diameter at both the ink jetting side and the ink channel side). Conventionally, however, there is no strictly determined ratio of the sectional area of the nozzle on the ink jetting side to that on the ink channel side. That ratio can be disproportionately large on one ink jet printer head and inordinately small on another. As a result, the jet speed of ink droplets, and hence the print speed, may vary from one ink jet printer head 1 to another. Such speed discrepancies can lead to a deterioration of print quality with ink jet printer heads, rendering them nonconducive to mass-production.
On the same ink jet printer head 1, the ratio of the sectional area of the nozzle on the ink jetting side to that on the ink channel side can vary significantly from one individual nozzle to another. This means that the jet speed of ink droplets can vary from nozzle to nozzle on the same printer head. The jet speed discrepancies can lead to a serious deterioration of print quality with the ink jet printer head 1. In some cases, the printer head does not function outright. As a result, there can be many defective ink printer heads if the printer heads are mass-produced.
Furthermore, with the prior art ink jet apparatus, there is no definitely determined taper angle .theta. at which the diameter of the nozzle 32 is narrowed progressively from the ink channel side toward the ink jetting side. The taper angle can be disproportionately large on one ink jet printer head and inordinately small on another. As a result, the jet speed of ink droplets, and hence the print speed, may vary from one ink jet printer head 1 to another. Such speed discrepancies can lead to a deterioration of print quality with ink jet printer heads, rendering them nonconducive to mass-production.
On the same ink jet printer head 1, the nozzle taper angle can vary significantly from one individual nozzle to another 32. This means that the jet speed of ink droplets can vary from nozzle to nozzle 32 on the same printer head. The jet speed discrepancies can lead to a serious deterioration of print quality with the ink jet printer head 1. In some cases, the printer head does not function outright. As a result, there can be many defective ink printer heads where the printer heads are mass-produced.
With ink jet apparatuses, the minimum sectional area of the nozzle 32 must be greater than the maximum projected area of solid ink particles to ensure good ink jet performance. Conventionally, however, there is no fixedly determined ratio of the minimum sectional area of the nozzle to the maximum projected area of solid ink particles. Whereas there is little problem if the sectional area of the nozzles on their ink jetting side is sufficiently large compared with the maximum projected area of solid ink particles, an insufficient sectional area of the nozzles can change the jet speed of ink droplets due to the friction between the nozzles and solid ink particles. The varying jet speeds can also vary the print speed from one ink jet printer head 1 to another. Such speed discrepancies can lead to a deterioration of print quality with ink jet printer heads, rendering them nonconducive to mass-production.
On the same ink jet printer head 1, some nozzles 32 may have insufficient sectional areas compared with the maximum projected area of solid ink particles while others have sufficient sectional areas. This means that the jet speed of ink droplets can vary from one individual nozzle 32 to another on the same printer head. The jet speed discrepancies can lead to a serious deterioration of print quality with the ink jet printer head 1. In some cases, the printer head does not function outright. As a result, there can be many defective ink printer heads if the printer heads are mass-produced.